Permeable concrete



Nqv. 25, 1958 Q G. MANGOLD- ETAL Re. 24,570

PERMEABLE CONCRETE Original Filed Jan. 19, 1952 CASING I3 WELL BORE l0PERMEABLE 'CEME/VT l5 sEco/vo "CE/VENT LA YER l7 DRILLING MUD l6 GEORGEE. HANGOLD JAMES A. DYER JOHN T. HART INVENTORS.

hrToR/vEr United States Patent PERMEABLE CONCRETE George B. Marigold,Los Angeles, Calif., James A. Dyer, Kings Ferry, N. Y., and John T.Hart, Monrovia, Calif., assignors, by mesne assignments, to Florent H.Bailly, Pasadena, Calif.

Original No. 2,793,957, dated May 28, 1957, Serial No. 267,218, January19, 1952. Application for reissue February 21, 1958, Serial No. 719,986

3 Claims. (Cl. 106-86) Matter enclosed in heavy brackets II] appears inthe original patent but forms no part of this reissue specification;matter printed in italics indicates the additions made by reissue.

This invention relates to permeable concrete which is characterized by apermeability higher than that of a conventional concrete. The permeablematerial may be so compounded as to yield a permeability as much as fivethousand times that of present materials. The composition of theinvention is properly referred to as a concrete for the reason that itincludes an aggregate in addition to sand and cement and othercomponents.

Under many circumstances a permeable concrete would serve a highlyuseful function. One example of such a situation is oil well cementingand the invention is particularly described in relation to such use.Other uses for permeable concrete will become apparent as its propertiesare herein discussed.

In oil field parlance the word cement is used to include a true concreteas well as a neat cement and in conformity with the terminology of theart the material of the present invention, although a concrete, isreferred to as cement when describing its use in oil field practice.

In cementing oil wells, the usual practice is to pump a cement slurry(made of water and conventional inorganic cement, such as Portlandcement) down through the interior of the casing or pipe and force it upfrom the bottom into the annulus between the casing and the formation. Asufiicient amount of cement slurry is used so that this annulus isfilled to the desired height. The cement, when set, anchors and supportsthe casing, supports the formation and seals off formation zones fromintercontamination by fluids and gases. When hydrocarbon production isdesired from a particular zone, the casing and set cement opposite thatzone are gun-perforated and the oil and gas are recovered through theseperforations.

The conventional cement slurry for this use is, when composed of cementand water, referred to as neat cement. The cement may include othermaterials such as aggregates, particularly lightweight aggregates,dispersing agents, bentonite, pozzolans, accelerating or retardingchemicals, bridging agents, etc. Regardless of its composition thiscement has heretofore been relatively impermeable, having a permeabilityin the order of less than one millidarcy. Such cements and concretes arehereinafter referred to as impermeable cement as distinguishing from thepermeable concrete of the present invention.

There are many problems encountered in this method of oil wellcompletion. Among these is the fact that a cement slurry composedpredominantly of very fine particles may be unintentionally forced intothe producing formation and thereby reduce its permeability. Mechanicalor gun-perforation of the set cement may not reach the actual formation,and to avoid this difliculty necessitates provision of an undesirablysmall annulus between the casing and the formation. Other completionmeth;

' creasing the pumpability of the mixture.

ods have been developed in an attempt to improve these conditionsincluding gravel packing and pro-packed liners. Each of these methodshas characteristics peculiar to it, a discussion of which would serve nouseful purpose in this disclosure.

We have now discovered a concrete composition and a method of preparinga concrete, which, upon setting, will be permeable and which is found tobe more per meable in most cases than the formation which it contacts.For oil well completion and other problems hereinafter mentioned whereinextremely high compressive strength is not a requisite, the permeableconcrete of the invention is superior to conventional concretes inserving a purpose not presently duplicated.

It is difficult, if not impossible, to define the compo- I sition of aconcrete after setting, and hence the usual practice is to define thecement slurry compositionwhich, upon setting, results in a concrete ofthe properties desired. A concrete in accordance with the inventioncomprises, as a slurry, cement, water, a first aggregate of apredetermined particle size distribution, a second aggregate of apredetermined particle size distribution differing from that of thefirst aggregate and such as to result in a gap in the over-all particlesize distribution of the two aggregates, and a stabilizer which is, forpresent purposes, preferably a pozzolanic material.

Although not necessarily so limited, lightweight aggregates arepresently preferred because of their angular, irregular particleconfiguration and low density, these factors facilitating adhesion anduniformity. Lightweight aggregates may be classified as follows:

(1) Natural aggregates; pumice, scoria, volcanic cinders and volcanicash, diatomite, diatomaceous earth.

(2) Expanded aggregates (utilizing heat to accomplish expansion); clay,shale, slate, diatomaceous earth, perlite, obsidian, vermiculite.

(3) Expanded aggregates (utilizing cooling to accomplish expansion);blast furnace slag.

(4) Sintered aggregates; shale, clay, fly ash, slag. These aggregateshave a unit weight up to about pounds per cubic foot and a bulk specificgravity of from about 0.6 to 2.4 according to ASTM specifications. Aconcrete including such aggregates will have a cured weight of from 20to pounds per cubic foot as compared to a cured weight of or more poundsper cubic foot exhibited by concrete employing the more conventionalheavy aggregates.

A stabilizer," as the term is used in this application, refers tomaterials used for the purpose of preventing or minimizing segregationof the larger particles. This may be accomplished by finely dividedmaterials which, when distributed throughout the concrete slurry,increase the apparent viscosity (decreased slump) without de- Thedistribution of these fine particles and the improved consistency act toprevent segregation of the larger and heavier particles. There are manymaterials used in the industry for this purpose but we have found thatthe pozzolanic materials are to be preferred in the concrete of thepresent invention because of the increase in compressive strengthconsequent upon such use.

A pozzolan is defined as any siliceous and aluminous material, naturalor artificial, processed-or unprocessed, which contains constituents notcementitious in themselves but which will, in finely divided formand inthe presence of moisture, react with calcium hydroxide at ordinarytemperatures to form relatively stable and water insoluble compoundspossessing cementitious properties, i. e. setting up to a solid. Naturalpozzolans may be derived from volcanic rocks and include pumicites orvolcanic 'ashes, pumice or pumicestone, obsidiam'scoria,

listing intended as exclusive.

tulfs and some of the andesites, or they may be derived from rocks inwhich the silica has a high opaline content including diatomites ordiatomaceous earths, cherts, shale, clays and pure opal. Moreover,pozzolans'includefly ash or flue dust, certain boiler and furnace slags,burnt ground brick and by-products of certain industrial processes.

particle size distribution and another type of aggregate :maybe used inthe second particle size distribution.

Further, each range of aggregate particle size may comprisetwo or moredifferent materials if such practice ap- :pears expedient for economicor other'rea'sons.

Choice of'materials will be dictated in large measure by availabilityand economies which will vary from location to location.

The use of two aggregates of differing particle size, and whichtogetherleave a gap in the over-all particle size distribution, is veryimportant to the accomplishment of the objectives of the invention.

The particle size gap should encompass a range of at least 3 or 4 meshsizes, as for example the particle size range of from 7 to 9 meshinclusive. We have found that omission of this particular range ofaggregate particles results in a maximum resultant permeability. Thepermeability of the concrete may, in fact, be roughly predetermined byproper selection of the aggregate sizes; the omission of particles ofsmaller size than the above range resulting in a somewhat lowerpermeability. In general we prefer to employ a coarse aggregate having aminimum particle size in the range of from 6 to 10' mesh and a fineaggregate having a maximum particle size of from about 10 to 20 mesh,the two aggregates being selected such that there is a size rangebetween the aggregates of at least 3 mesh sizes in which there aresubstantially no aggregate particles.

Uniform particle size distribution in the ranges selected is desirable.Such uniform distribution facilitates adhesion and in so doing increasesthe strength of the resultant concrete.

It is also apparent that the characteristics of an aggregate play animportant part in achieving a highly permeable material since thelightweight aggregates produce a concrete of considerably greaterpermeability than do the so-called heavy aggregates. In addition, theheavy aggregates are susceptible to undesirable segregation when used insome of the proportions [required] set forth herein. These aggregatesare more difficult to hold together in a uniform mass because of theirgreater density and generally smoother and more regular particleconfiguration.

The following table sets forth the various ingredients of a slurry inaccordance with the invention, resulting in-a permeable set concrete andthe permissible and pre- 7 ferred ranges of the proportioning of thesematerials.

TABLE I Permissible Preferred Range in Composi- Component Parts by tionin Weight Parts by Weight Cement 1 1 .Water 1. 5 to 2. 5 2 Pozzolan(stabilizer) 0. to 0. 40 .33 Aggregate:

(a) 10 to 100 mesh 1.0 to 2. 0 1. 65

an (b) 3 to 6 mesh 4.0 to 7 5. 75

A concrete having a slurry composition-as indicated as preferred in theabove table, will have essentially the following properties:

TABLE II A. Average properties of slurry:

Density:

'12 lbs. per-gal. lbs. per cu. ft. 'Void'spacez 25% Yield:

1 gal. per lb. of cement 94. gals. per sack of cement 12 /2 cu. ft. persack of cement B. Properties of set cement:

Permeability: 8.5 to 9.5 darcies 3-day compressive strength: 400 p. s.i. 17-day compressive strength (ambient curing):

1000p. s. i.

As mentioned above, a concrete of somewhat lower permeability may beproduced if desired by shifting the excluded particle size range ofaggregate. Thus a first aggregate having a minimum particle size ofapproximately8 mesh and a second aggregate having a particle sizedistribution of from about 20 to mesh may be used inv place of theaggregates identified in Table -I. Other variations are also possibleand even desirable under certain circumstances.

Apresently preferred method for compounding the slurry in accordancewith the invention involves the 'following steps:

(1) Thoroughly mix the dry cement and pozzolan.

even distribution difficult with wet material.

(2) Tho-roughly mix the cement-stabilizer mixture 'with aggregate.

(3) Add the required amount of water and mix the entire slurry.

7 Of the many forms of stabilizers in general and p02- z'olans inparticular available for such use, an oil impregnated diatomaceousearth, calcined and ground is presently preferred and the same materialin the larger mesh sizes ispreferred as a lightweight aggregate.

Preferred practice of using the permeable concrete of the invention inoil well completion is best described with reference to the accompanyingdrawing which is a verticalsection'through the lower portion of a wellbore. In the drawing, a well bore 10 is shown traversing formations 12,and is provided with the usual casing 13 projecting just short of thebottom of the bore. In completing a well of this type in accordance withone method of the invention, a layer 14 of conventional cement orconcrete slurry is pumped into the annulus defined 'bythe casing andwell bore a'ndis followed by a layer 15 of permeable concrete slurrycompounded as herein described, which is in turn followed by a layer 16of a viscous oil base drilling fluid and another layer 17 ofconventional concrete slurry. The fluid stream composed of theconventional slurry, permeable cement slurry, drilling mud andconventional slurry, is positioned with respect to its height in theannulus in the usual manner by controlling the quantities of each pumpedinto the well bore.

The oil base drilling mud used for this purpose is preferably composedof an asphalt-free crude or fuel oil base'containing an oil solublemetallic ester. As'phaltic materials are not objectionable for use atlow bottom hole temperatures but are objectionable for use at'high'tem-'per-atures-for reasons hereafter apparent. Weighting materials arepreferably left out of the mud as adversely affecting the mud densityfor this specific purpose.

The oil base drilling mud migrates into the void spaces of-thepermeableconcrete slurry while setting is taking 7 Y. 75 place.Inthis-manne'r-intrusion-of the adjacent regular cement slurry isprevented, it being apparent that such intrusion would materially reducethe'resultant permeability. The amount of mud used should be calculatedat approximately that required to fill these voids so that the trailinglayer of conventional slurry will be contiguous to the permeablematerial. When the casing is perforated the thus occluded mud finds itsway out of the permeable layer. At high temperatures any asphalticmaterials in the mud tend to polymerize and in so doing adversely affectthe permeability of the concrete. The induced intrusion of the mud hasthe further purpose of preventing intrusion of formation fluids whichmay leach or otherwise interfere with the structure of the permeableslurry.

The described permeable cement in slurry and cured form exhibits thefollowing properties and advantages when used in the manner describedfor oil Well completion:

(1) It is a thick but pumpable slurry with little tendency towardssegregation.

(2) It contains too small a proportion of fines and those that arepresent are so tightly held that formation plugging is avoided.

(3) It will fill any size hole drilled for efficient production or anysizable fractures and crevices, and hence support the fractures andcrevices, and will not interfere with the advantageous permeabilitythereof.

(4) It sets with sufficient strength to support casing and formation andit sets well under high temperatures and pressures which may beencountered in a well bore.

(5) It sets in the presence of oil or oil base fluid,.

leaving the concrete oil wet and providing better flow characteristicsfor oil recovery.

(6) A high permeability throughout the mass is preserved after it is setsince no reorientation takes place during setting.

(7) The liner need not be perforated until after the slurry has set,which allows the use of large sized perfo rations.

As mentioned, the slurry may be preceded by a regular cement slurryfollowed by the oil base drilling fluid and lastly followed by anotheramount of regular cement slurry. The latter supports the permeablecement and may be used to shut off the lower formation zones ifdesirable. Care should be taken that the density of the leading slurrybe at least as low as that of the permeable concrete, and that itsviscosity be sufli'cient to prevent segregation.

As an alternative procedure the entire bottom hole may be filled withpermeable concrete. In such application the casing is drilled out afterthe concrete sets and a thin slurry of regular cement is pumped in topermeate a short distance into the permeable concrete. This procedureseals off and strengthens the exposed surfaces of the permeablematerial.

The invention has thus far been described particularly with relation tothe use of the defined permeable concrete in oil well completiontechniques. This is a vast field and one in which a permeable concretemay well revolutionize present practices. It is even likely that thediscovery of this type of concrete may enable elimination from oil wellsof the conventional casing. Such an eventuality would, of course, savemillions of dollars and large amounts of steel.

The permeable concrete has other very significant potentialities. Fordrainpipes, non-structural surfaces, gutters and the like, the propertyof permeability is very beneficial. One prime example is tennis courts,where permeability to water would permit the court to dry after a rainor washing much faster than is the case with impermeable concretes. Indrainpipes and for street gutters and other drainage systems, permeationof water through the concrete would reduce the loading of the system andwould also return to the earth water which is much needed in manylocalities and which is now generally dumped in the ocean. Many otheruses for the permeable concrete of the invention will undoubtedly occurwhen its properties become generally known.

We claim:

1. A concrete characterized by a relatively high permeability to liquidswhich as a slurry consists essentially of approximately 1 part ofPortland cement, 0.10 to 0.40 part of a pozzolan, 4.0 to 7.0 parts of afirst [lightweight] aggregate having a particle size distribution offrom about 3 to about 6 mesh, 1.0 to 2.0 parts of a second [lightweight]aggregate having a particle size distribution of from about 10 mesh toabout mesh, there being substantially no aggregate particles in the sizerange of from about 7 to about 9 mesh, and water.

2. A concrete characterized by a relatively high perm-eability toliquids which as a slurry consists essentially of approximately 1 partof Portland cement, 0.10 to 0.40 part of a pozzolan, up to 7.0 parts ofa coarse [lightweight] aggregate having a minimum particle size of fromabout 6 to about 10 mesh, up to 2.0 parts of a fine [lightweight]aggregate having a maximum particle size of from about 10 to about 20mesh, the two aggregates having respective particle size distributionssuch that there is a range of at least 3 mesh sizes between the coarseand fine aggregates in which there are substantially no aggregateparticles, and water.

3. A concrete characterized by a relatively high permeability to liquidswhich as a slurry consists essentially of approximately 1 part ofPortland cement, 0.10 to 0.40 part of a pozzolan, 4.0 to 7.0 parts of afine [lightweight] aggregate having a maximum particle size of about 3mesh, 1.0 to 2.0 parts of a fine [lightweight] aggregate having amaximum particle size in the range of 10 to 20 mesh, the minimumparticle size of the coarse aggregate and the maximum particle size ofthe fine aggregate being controlled such that there is a range of from 3to 4 mesh sizes between the two aggregates in which there issubstantially no aggregate particles, and water.

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